Which instrument did Louis Armstrong famously play?

The trumpet - though he began on cornet, and the switch was partly about wanting to be heard over a bigger band. What he actually changed was more fundamental than an instrument: before Armstrong, jazz was largely collective improvisation with everyone weaving at once, and he made it a music of soloists.

The Hot Five and Hot Seven recordings of the late 1920s are where it happens, and the moment usually singled out is the opening cadenza of West End Blues in 1928 - twelve seconds of unaccompanied trumpet that musicians have been analysing ever since. He also more or less invented scat singing on record, reportedly after dropping the lyric sheet mid-take.

His later reputation was complicated by his own popularity. Younger black musicians in the 1950s and 60s found the grinning, handkerchief-waving stage persona embarrassing, and Miles Davis and others said so. Armstrong then cancelled a State Department tour in 1957 and publicly called Eisenhower two-faced and gutless over the government's failure to enforce school desegregation in Little Rock - at real cost to his bookings, and from a position nobody expected him to take.